Summary: The importance of the nitrate () transporter for yield and nitrogen‐use efficiency (NUE) in rice was previously demonstrated using map‐based cloning. In this study, we enhanced the expression of theOsNRT2.1gene, which encodes a high‐affinitytransporter, using a ubiquitin (Ubi) promoter and the‐inducible promoter of theOsNAR2.1gene to driveOsNRT2.1expression in transgenic rice plants. Transgenic lines expressingpUbi:OsNRT2.1orpOsNAR2.1:OsNRT2.1constructs exhibited the increased total biomass including yields of approximately 21% and 38% compared with wild‐type (WT) plants. The agriculturalNUE(ANUE) of thepUbi:OsNRT2.1lines decreased to 83% of that of theWTplants, while theANUEof thepOsNAR2.1:OsNRT2.1lines increased to 128% of that of theWTplants. The dry matter transfer into grain decreased by 68% in thepUbi:OsNRT2.1lines and increased by 46% in thepOsNAR2.1:OsNRT2.1lines relative to theWT. The expression ofOsNRT2.1in shoot and grain showed thatUbienhancedOsNRT2.1expression by 7.5‐fold averagely andOsNAR2.1promoters increased by about 80% higher than theWT. Interestingly, we found that theOsNAR2.1was expressed higher in all the organs ofpUbi:OsNRT2.1lines; however, forpOsNAR2.1:OsNRT2.1lines,OsNAR2.1expression was only increased in root, leaf sheaths and internodes. We show that increased expression ofOsNRT2.1, especially driven byOsNAR2.1promoter, can improve the yield and NUE in rice.

Biochars are complex heterogeneous materials that consist of mineral phases, amorphous C, graphitic C, and labile organic molecules, many of which can be either electron donors or acceptors when placed in soil. Biochar is a reductant, but its electrical and electrochemical properties are a function of both the temperature of production and the concentration and composition of the various redox active mineral and organic phases present. When biochars are added to soils, they interact with plant roots and root hairs, micro-organisms, soil organic matter, proteins and the nutrient-rich water to form complex organo-mineral-biochar complexes Redox reactions can play an important role in the development of these complexes, and can also result in significant changes in the original C matrix. This paper reviews the redox processes that take place in soil and how they may be affected by the addition of biochar. It reviews the available literature on the redox properties of different biochars. It also reviews how biochar redox properties have been measured and presents new methods and data for determining redox properties of fresh biochars and for biochar/soil systems.

Biochar-based compound fertilizers (BCF) and amendments have proven to enhance crop yields and modify soil properties (pH, nutrients, organic matter, structure etc.) and are now in commercial production in China. While there is a good understanding of the changes in soil properties following biochar addition, the interactions within the rhizosphere remain largely unstudied, with benefits to yield observed beyond the changes in soil properties alone. We investigated the rhizosphere interactions following the addition of an activated wheat straw BCF at an application rates of 0.25% (g·g^-1 soil), which could potentially explain the increase of plant biomass (by 67%), herbage N (by 40%) and P (by 46%) uptake in the rice plants grown in the BCF-treated soil, compared to the rice plants grown in the soil with conventional fertilizer alone. Examination of the roots revealed that micron and submicron-sized biochar were embedded in the plaque layer. BCF increased soil Eh by 85 mV and increased the potential difference between the rhizosphere soil and the root membrane by 65 mV. This increased potential difference lowered the free energy required for root nutrient accumulation, potentially explaining greater plant nutrient content and biomass. We also demonstrate an increased abundance of plant-growth promoting bacteria and fungi in the rhizosphere. We suggest that the redox properties of the biochar cause major changes in electron status of rhizosphere soils that drive the observed agronomic benefits.

Summary: The nitrate () transporter has been selected as an important gene maker in the process of environmental adoption in rice cultivars. In this work, we transferred another native OsNAR2.1 promoter with driving OsNAR2.1 gene into rice plants. The transgenic lines with exogenous pOsNAR2.1:OsNAR2.1 constructs showed enhanced OsNAR2.1 expression level, compared with wild type (WT), and ¹⁵N influx in roots increased 21%–32% in response to 0.2 mm and 2.5 mm and 1.25 mm ¹⁵NH₄¹⁵NO₃. Under these three N conditions, the biomass of the pOsNAR2.1:OsNAR2.1 transgenic lines increased 143%, 129% and 51%, and total N content increased 161%, 242% and 69%, respectively, compared to WT. Furthermore in field experiments we found the grain yield, agricultural nitrogen use efficiency (ANUE), and dry matter transfer of pOsNAR2.1:OsNAR2.1 plants increased by about 21%, 22% and 21%, compared to WT. We also compared the phenotypes of pOsNAR2.1:OsNAR2.1 and pOsNAR2.1:OsNRT2.1 transgenic lines in the field, found that postanthesis N uptake differed significantly between them, and in comparison with the WT. Postanthesis N uptake (PANU) increased approximately 39% and 85%, in the pOsNAR2.1:OsNAR2.1 and pOsNAR2.1:OsNRT2.1 transgenic lines, respectively, possibly because OsNRT2.1 expression was less in the pOsNAR2.1:OsNAR2.1 lines than in the pOsNAR2.1:OsNRT2.1 lines during the late growth stage. These results show that rice NO₃^– uptake, yield and NUE were improved by increased OsNAR2.1 expression via its native promoter.

OsNRT1.1a is a low‐affinity nitrate (NO₃⁻) transporter gene. In this study, another mRNA splicing product, OsNRT1.1b, putatively encoding a protein with six transmembrane domains, was identified based on the rice genomic database and bioinformatics analysis. OsNRT1.1a/OsNRT1.1b expression in Xenopus oocytes showed OsNRT1.1a‐expressing oocytes accumulated ¹⁵N levels to about half as compared to OsNRT1.1b‐expressing oocytes. The electrophysiological recording of OsNRT1.1b‐expressing oocytes treated with 0.25 mM NO₃⁻ confirmed ¹⁵N accumulation data. More functional assays were performed to examine the function of OsNRT1.1b in rice. The expression of both OsNRT1.1a and OsNRT1.1b was abundant in roots and downregulated by nitrogen (N) deficiency. The shoot biomass of transgenic rice plants with OsNRT1.1a or OsNRT1.1b overexpression increased under various N supplies under hydroponic conditions compared to wild‐type (WT). The OsNRT1.1a overexpression lines showed increased plant N accumulation compared to the WT in 1.25 mM NH₄NO₃ and 2.5 mM NO₃^– or NH₄⁺ treatments, but not in 0.125 mM NH₄NO₃. However, OsNRT1.1b overexpression lines increased total N accumulation in all N treatments, including 0.125 mM NH₄NO₃, suggesting that under low N condition, OsNRT1.1b would accumulate more N in plants and improve rice growth, but also that OsNRT1.1a had no such function in rice plants.

Nitrogen (N) plays a critical role in plant growth and productivity and PTR/NRT1 transporters are critical for rice growth. In this study, OsPTR6, a PTR/NRT1 transporter, was over-expressed in the Nipponbare rice cultivar by Agrobacterium tumefaciens transformation using the ubiquitin (Ubi) promoter. Three single-copy T2 generation transgenic lines, named OE1, OE5 and OE6, were produced and subjected to hydroponic growth experiments in different nitrogen treatments. The results showed the plant height and biomass of the over-expression lines were increased, and plant N accumulation and glutamine synthetase (GS) activities were enhanced at 5.0mmol/L NH4(+) and 2.5mmol/L NH4NO3. The expression of OsATM1 genes in over-expression lines showed that the OsPTR6 over expression increased OsAMT1.1, OsATM1.2 and OsAMT1.3 expression at 0.2 and 5.0mmol/L NH4(+) and 2.5mmol/L NH4NO3. However, nitrogen utilisation efficiency (NUE) was decreased at 5.0mmol/LNH4(+). These data suggest that over-expression of the OsPTR6 gene could increase rice growth through increasing ammonium transporter expression and glutamine synthetase activity (GSA), but decreases nitrogen use efficiency under conditions of high ammonium supply.